In the molding of certain synthetic-resin objects, it is necessary to mix the several components to be molded in such a manner that the relative proportions of the substances are extremely accurately controlled while the substances are maintained out of contact with each other until the last possible moment. Thus, when molding an epoxy or certain thermosetting resins, the components should be fed in exactly controlled doses to a mixing recipient and thence to the mold, remaining for as little time as possible in the mixing recipient to avoid reaction of the components and curing of the resin.
The standard systems for doing this merely have pressurized supplies of the degassed components which are connected via respective conduits having respective solenoid valves to the mixing recipient. An electronic, normally computer-controlled, command unit opens and closes these valves so that the products are exactly dosed into the mixing recipient. Such an arrangement normally requires that the product be tested extensively during setting-up of the machine, and thereafter that the product be sampled periodically in order to insure that it has the components in proper proportions.
Another arrangement uses stroke-type dosing pumps of the positive-displacement type. The stroke length for each such pump is limited to correspond to the respective portion it is to deliver. Thus, all of the dosing pumps are actuated simultaneously to deliver the components. Such an arrangement normally requires lengthy heated conduits between the dosing pumps and the mixing equipment, and other relatively complex mechanism in order to insure proper functioning.
The known machines are all relatively complex, and therefore quite expensive. Typically, the machines can only be readjusted for different components in different proportions by qualified personnel and after extensive down time. Many require extensive heated conduits between the dosing pump and the mixing recipient to maintain the components in liquid form between the mixing recipient and the dosing pumps which are normally at some distance from one another.